Small but powerful, compact trenchers are mainstays on many residential and commercial jobsites. They are most often used for excavating short run trenches for utilities placement and drainage in constricted operating areas.
Walk-behind units are the most common in these classes, although walk-beside models are used extensively as well. Beyond operator accommodation, there are hydrostatic drive units, which use hydraulic pumps to propel the unit’s drive system and rotate the cutting chain, and mechanical-drive trenchers that use a conventional drive chain or belts to initiate those actions.
Two-wheel drive units are common, although four-wheel-drive walk-behind trenchers are available for contractors trenching in soft ground conditions. Hydrostatic trenchers deliver horsepower to the cutting chain and wheels more efficiently, and tend to be smoother to operate. Mechanical drive train units are lighter and cheaper to purchase, but more expensive to maintain.
Compact trenchers typically consist of three basic operating systems. The ground drive moves the machine across the soil, either to transport the unit or to pull it forward while trenching. The unit’s trenching articulation is the business end of the trencher and usually consists of drive traction, boom and chain-drive control functions. Finally, a spoil-handling auger at the base of the boom windrows trenched soil out and to the side of the trench for easy backfilling later.
Generally speaking, because of the short runs they are designed for, most contractors only keep or rent one compact trencher for the jobs they have to complete. Contractors who use more than one compact trencher on a jobsite do so because they have multiple short-run trenches that need to be cut simultaneously. Using several compact trenchers for one long run is usually not practical and can probably be handled more efficiently by a ride-on unit.
Proper chain tension is vital. Loose or tight chains not only rob you of horsepower in the trench, they can significantly shorten a trencher’s lifespan.
Scoop or gouge? Optimize trencher teeth to match soil types
Compact trenchers are designed to handle a wide variety of soil types, from sandy loam to material studded with hard rock, and are effective at digging trenches approximately 36 inches deep. “We offer some units that will allow you to go a little deeper than that,” notes Brian Kenkel, product specialist, Vermeer. “But if you need to excavate ditches much deeper than that, you probably need to move up to a ride-on trencher.”
Compact trencher boom lengths are set for specific depths. “But remember that boom length has a maximum depth, no matter how deep you set it up to run,” cautions Brett Bolay, senior product manger, trenching, Ditch Witch. “A walk-behind trencher boom uses the trench space itself to help clean dirt out of the ditch. So if you try and trench at a very shallow depth with a very long boom, you will rob the machine of performance since the spoil won’t be efficiently removed. So matching proper boom length to the desired depth is very important. If you want 20 inches of cover and you’ve got a 20-inch boom on the machine, you’ll get along fine.”
Once you know the depth, length and width of the trench you need excavated, your next concern – and your primary concern for high production – is the soil type you’ll be digging in. “Soil conditions will dictate chain configuration, ground speed when trenching and safety considerations,” says George Whitaker, platform marketing manager, Case Construction Equipment. “Soil types can also affect depth and width considerations, and even spoil management during the course of a compact trenching operation.”
Ensuring a productive trenching job means correctly spec’ing the chain configurations for your machine. “Chain configurations vary,” Whitaker says, “and normally depend on the soil’s compaction level and its makeup (including how much rock is present). To meet the wide array of soil types found around the country, manufacturers offer trencher chains ranging from standard cup type configurations for sandy soil types, to carbide tipped chains and even rock wheels to trench in severe ground conditions.”
Although soil conditions can vary widely in a single geographic location, those areas are rare. Most contractors will be able to spec one type of cutting teeth for their trencher and use the machine effectively in their normal area of operations. Your local trencher dealer is the best source of information when it comes to spec’ing cutting teeth for your chain, but there are some general rules worth keeping in mind as you prepare a trencher for your fleet.
The chain’s teeth do the actual digging work. Cup teeth are the most common tooth style used today. They may be placed alternately with other types of teeth on a chain, or may be the only type used in very soft soil. As their name implies, cup teeth scoop dirt out of the ground as the chain rotates around the boom.
Carbide teeth are designed for tougher soils, including some with significant rock content. Carbide teeth not only increase trenching production in tougher soil types, but also offer great durability and extended life in normal digging conditions.
Most carbide and cup teeth are bolted to the chain. Some carbide teeth, commonly called “shark” teeth, are welded directly to the chain for even more durability. It’s important to note that when bolt-on teeth wear down or break, they can be replaced by simply bolting a new tooth onto the chain. Replacement shark teeth must be welded onto a chain when the originals wear out or break.
Soil type is your primary concern when preparing a trencher for a jobsite. Your local dealer can provide you with the correct chain and cutter configuration to optimize performance.
Take care to retain proper patterns when replacing teeth and cups
If you take it upon yourself to replace chain teeth you should remember that the teeth are set in specific patterns for optimal cutting performance. “Be aware that you need to replace them in the same position the old tooth was in,” Bolay warns. “There are ‘right’ and ‘left’ designated teeth and it’s not unheard of for someone to put them on a chain backwards, which wreaks havoc with your production.” In addition, you must take care to preserve the original tooth pattern if you want the trencher to remain productive. Tooth patterns aren’t random. A lot of research is done to make sure a particular pattern will deliver optimum performance in specific types of soil.
Bolay says failing to replace worn-out teeth is the single most common error he sees operators make when he visits jobsites. “Once teeth reach the end of their useful life, it’s like trying to cut a steak with a dull knife,” he says. “The machine is forced to work twice as hard to make a cut. All that added stress isn’t good for the trencher, and you’ll eventually end up tearing something else up on the machine.” Good, sharp, digging teeth not only help the productivity of the machine, they also reduce overall wear and tear and play a huge role in extending the life of the trencher.
And don’t let cost deter you from replacing worn-out teeth, Kenkel says. “Cutter and chain replacement is quite inexpensive if you stay on top of it,” he says. Still, you can save yourself some money and maximize your investment by taking worn cup teeth and moving them to the inner cutters of the chain when they begin to show excessive wear.
“Those worn teeth can still be productive on the inside of the chain where the cutting action is not as abrasive,” Kenkel says. “Be sure to replace the worn teeth with new cup cutters. You’ll still have an effective chain, and you’ll get more life out of those cup teeth.”
Check chain tension often for longer machine life
Once they’ve settled on the proper teeth for the job at hand, skilled operators will take a minute to check the chain’s tension before putting a compact trencher to work. Proper chain tension is vital for optimum machine performance, and yet Kenkel says it’s one of the most commonly overlooked aspects of compact trencher usage.
A loose chain causes the unit’s digging ability to drop off dramatically, Kenkel says. Worse, the loose chain creates a lot of unnecessary vibration, which can damage the boom or the chain because it is not cutting efficiently. A loose chain may also damage the trencher’s wear strip. “The cutter has enough travel to bend backwards in the ditch,” Kenkel explains. “So the chain doesn’t run in a straight line when loose. It ends up warping into a D-shaped pattern and starts to dig into the boom structure itself.”
A chain that’s too tight may rob your trencher of productivity, mainly because its torsion takes horsepower away from the cutting edge of the boom. Although most operators develop a feel for proper chain tension, Kenkel says there’s an easy way to spot-check your trencher and make certain it’s good to go. “Place the boom horizontal to the ground,” he says, “and measure any slack in the chain as it hangs off the bottom part of the boom.” If the tension is right, you should be able to slide either two or three fingers between the bottom of the boom and the chain. That’s an easy sight gauge that translates to approximately 1-1/2 inches of slack on the chain, which is right where it needs to be for productive operation.
Routine maintenance and transportation are two final areas Kenkel says contractors should be concerned with if they have compact trenchers in their fleets. “I see a lot of trenchers get torn up simply by being poorly bound and hauled down the highway,” he says. “When transporting your trencher, haul it on a trailer with a good suspension. Simple road vibrations and impacts are very hard on these units and cause a lot of premature wear.”
At the same time routine maintenance must not be overlooked if you expect long life from your machine. Keeping a tight preventive maintenance schedule – particularly the trencher’s air cleaner and oil changes – should be a high priority for you. These machines work in very hot, dirty and dusty environments. Keeping the engines clean is an easy way to make sure that trencher performs effectively for a long time on your jobsites.
Proper chain tension is vital. Loose or tight chains not only rob you of horsepower in the trench, they can significantly shorten lifespan.